Copolymer for use in alkene-alkane separation membranes

ABSTRACT

Described herein are copolymers derived from certain perfluorinated sulfonyl fluoride monomers, cyclic or cyclizable perfluorinated monomers, and one or both of ethylene and/or vinyl fluoride. Group 11 metal sulfonate ionomers of these copolymers, especially silver ionomers, are useful in membranes which separate olefins from alkanes.

GOVERNMENT RIGHTS

Support was provided under Department of Energy awards of DE-SC0004672and DE-SC0007510. The U.S. government has rights in this patentapplication.

FIELD OF THE INVENTION

This invention describes copolymers which can be made into Group 11metal ionomer which are useful in membranes for the separation ofalkenes and alkanes.

TECHNICAL BACKGROUND

Nonporous, but permeable, membranes have been used to separate varioustypes of chemicals for a long time. For instance certain types ofsemipermeable membranes are used to separate water from seawater, oroxygen from nitrogen, or carbon dioxide from methane, or alkenes fromalkanes.

The separation of alkenes from alkanes can be accomplished using asilver ionomer of a fluorinated polymer. Usually, perhaps becausefluoropolymers are more stable to oxidation than unfluorinated polymers,the Group 11 metal ionomers of fluorinated polymers are often morestable than unfluorinated polymers. Also polymers which contain fluorosubstituents near, for instance sulfonic acid or carboxyl groups tend tobe very strong acids (sometimes called “super acids”), the silver saltsmay be more stable.

In oil refineries or olefin polymerization plants sometimes one hasmixtures of alkenes and alkanes and one desires to separate the alkenesfrom the alkanes. This may be relatively easy if these two types ofcompounds have significant differences in boiling points, but separationof such compounds with similar boiling points is more difficult andexpensive, especially if the boiling points are lower in temperature.For instance propane boils at −44.5° C. and propylene boils at −47.8° C.Separation of these two compounds by cryogenic distillation is veryexpensive because of high energy costs. Therefore cheaper, less energyintensive methods of separation are desirable.

U.S. Pat. No. 5,191,151 to Erikson et al. describes the separation oflower alkenes (containing 2 to 4 carbon atoms) from lower alkanes(containing one to six carbon atoms) using a membrane which is a silverionomer of a polymer of tetrafluoroethylene (TFE) and a perfluorovinylether containing a terminal precursor group to a sulfonic acid. Thepresently claimed copolymers are not mentioned in Eriksen.

U.S. Patent Application 2015/0025293 to Feiring et al. describes the useof a membrane which is a silver ionomer of a perfluorinated polymer. Thepresently claimed copolymers are not mentioned in Feiring.

SUMMARY OF THE INVENTION

This invention concerns a copolymer, comprising repeat units derivedfrom a monomer of the formula CF₂═CF(OR_(f))SO₂F, one or more cyclic orcyclizable perfluorinated monomers, and one or both of vinyl fluorideand ethylene, wherein R_(f) is perfluoroalkylene or ether containingperfluoroalkylene having 2 to 20 carbon atoms, and provided that repeatunits derived from CF₂═CF(OR_(f))SO₂F are at least one mole percent oftotal repeat units, units derived from one or more cyclic or cyclizableperfluorinated monomers are at least 1 mole percent of total repeatunits, and repeat units derived from both ethylene and vinyl fluorideare in total at least 1 percent of total repeat units.

Also disclosed are copolymers in which the —SO₂F group has beenconverted to other groups such as sulfonic acid or metal sulfonate salt,membranes comprising one or more layers comprising such copolymers, anda method of separating alkenes from alkanes using such membranes.

DETAILS OF THE INVENTION

Herein certain terms are used and they some of the are defined below.

By a “driving force” in the separation of the alkene and alkane in thegaseous state is generally meant that the partial pressure of alkene onthe first (“feed”) side of the membrane is higher than the partialpressure of alkene on the second (“product”) side of the membrane. Forinstance this may be accomplished by several methods or a combinationthereof. One is pressurizing first side to increase the partial pressureof alkene on the first side, second is sweeping the second side by inertgas such as nitrogen to lower the partial pressure of the alkene on thesecond side, and third is reducing pressure of second side by vacuumpump to lower the partial pressure of the alkene on the second side.These and other known methods in the art of applying a driving force maybe used.

This may be quantified for a separation of gases to some extent by amathematical relationship:

Q _(a) αF _(a)(P1_(a) −P2_(a))

wherein Q_(a) is the flow rate of component “a” through the membrane,F_(a) is the permeance of component a through the membrane, P1_(a) isthe partial pressure on the first (feed) side, and P2_(a) is the partialpressure on the second (product) side.

By a membrane containing one or more Group 11 metal ionomers is meant amembrane comprising a thin nonporous layer of the metal ionomer and oneor more other polymeric layers which physically support or reinforce theGroup 11 metal ionomer layer. Preferably the Group 11 metal ionomerlayer is about 0.1 μm to about 1.0 μm thick, more preferably about 0.2μm to about 0.5 μm thick. The other layer(s) should preferably berelatively permeable to the alkenes and alkanes to be separated, and notthemselves have much if any tendency to separate alkenes and alkanes.

The Group 11 metal ionomer described here is prepared from a copolymercomprising repeat units derived from a compound of the formulaCF₂═CF(OR_(f))SO₂F, one or more cyclic or cyclizable perfluorinatedmonomers, and one or both of vinyl fluoride (VF) and ethylene (E),wherein R_(f) is perfluoroalkylene or ether containing perfluoroalkylenehaving 2 to 20 carbon atoms. The resulting polymer contains sulfonyl flurode groups (—SO₂F) which may be readily converted to sulfonic acid, ametal sulfonate salt, etc. see for instance U.S. patent application Ser.No. 14/334,605, U.S. Provisional Applications 62/159,646, 62/159,668,and 62/262,169 (now PCT applications ______, respectively), A. van Zyl,et al., Journal of Membrane Science, 133, (1997), pp. 15-26, O. I.Eriksen, et al., Journal of Membrane Science, 85 (1993), pp. 89-97, andA. J. van Zyl, Journal of Membrane Science, 137 (1997), pp. 175-185, andU.S. Pat. No. 5,191,151, all of which are hereby included by reference.Thus the repeat unit in the polymer derived from CF₂═CF(OR_(f))SO₂F maybe represented as

wherein Y is fluorine, —OH, or —OM wherein M is a metal cation,preferably univalent metal cation. Preferred metal cations are alkalimetal cations such as Na⁺ and/or K⁺, and Group 11 metal cations such asCu⁺ and/or Ag⁺. Group 11 metal cations are preferred and silver isespecially preferred.

Another type of useful monomer is a perfluorinated cyclic or cyclizablemonomer. By a cyclic perfluorinated monomer is meant a perfluorinatedolefin wherein a double bond of the olefin is in the ring or the doublebond is an exo double bond wherein one end of the double bond is at aring carbon atom. By a cyclizable perfluorinated monomer is meant anoncyclic perfluorinated compound containing two olefinic bonds, andthat on polymerization forms a cyclic structure in the main chain of thepolymer (see for instance N. Sugiyama, Perfluoropolymers Obtained byCyclopolymereization and Their Applications, in J. Schiers, Ed., ModernFluoropolymers. John Wiley & Sons, New York, 1997, p. 541-555, which ishereby included by reference). Such perfluorinated cyclic and cyclizablecompounds include perfluoro(2,2-dimethyl-1,3-dioxole),perfluoro(2-methylene-4-methyl-1,3-dioxolane), a perfluoroalkenylperfluorovinyl ether, and2,2,4-trifluoro-5-trifluoroimethoxy-1,3-dioxole. Preferably repeat unitsderived from one perfluorinated cyclic or cyclizable monomer are presentin the polymer. Of course the exact structure of a repeat unit from aperfluorinated cyclic or cyclizable monomer will depend on theparticular monomer used.

Repeat units derived from ethylene and vinyl fluoride are those usuallyobtained in such similar fluorinated polymers, —CH₂CH₂— and —CH₂CHF—,respectively.

At least one mole percent (preferably at least about 5 percent) of therepeat units present in the polymer are derived from each ofCF₂═CF(OR_(f))SO₂F, and one or more cyclic or cyclizable perfluorinatedmonomers. At least one percent (preferably at least about 5 percent) ofthe repeat units are derived from the total repeat units derived from Eand VF. Preferably repeat units derived from CF₂═CF(OR_(f))SO₂F areabout 10 mole percent to about 40 mole present of total repeat units inthe polymer, more preferably about 25 mole percent to about 40 molepercent. Preferably repeat units derived from one or more cyclic orcyclizable perfluorinated monomers are about 5 mole percent to about 30mole present of total repeat units in the polymer, more preferably about10 mole percent to about 25 mole percent. Preferably the total repeatunits derived from E and VF are about 10 mole percent to about 60 molepresent of total repeat units in the polymer, more preferably about 20mole percent to about 50 mole percent. In one preferred form all of therepeat units in the polymer consist essentially of those derived fromCF₂═CF(OR_(f))SO₂F, one or more cyclic or cyclizable perfluorinatedmonomers, and one or both of E and VF. In one preferred form, thecopolymer consists essentially of repeat units derived fromCF₂═CF(OR_(f))SO₂F, one or more cyclic or cyclizable perfluorinatedmonomers, and repeat units derived from one of VF and/or E

Other useful comonomers include tetrafluoroethylene, vinylidene fluorideand chlorotrifluoroethylene.

Preferred specific monomers of the type CF₂═CF(OR_(f))SO₂F includeCF₂═CFOCF₂CF₂SO₂F, CF₂═CFOCH₂CF₂CF₂SO₂F, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F,CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F and CF₂═CFOCF₂CF₂SO₂F for theCF₂═CF(OR_(f))SO₂F type monomer, and preferred cyclic or cyclizableperfluorinated monomers include perfluoro(2,2-dimethyl-1,3-dioxole),perfluoro(2-methylene-4-methyl-1,3-dioxolane), a perfluoroalkenylperfluorovinyl ether, and2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole, andperfluoro(2,2-dimethyl-1,3-dioxole) is more preferred. Preferably one ofeach type of these preferred monomer, a sulfonyl fluoride containingmonomer and a preferred cyclic or cyclizable perfluorinated monomer iscopolymerized with one or both of VF and E to form a preferredcopolymer. It is to be understood that any of the preferred monomersmentioned in this paragraph can be combined with another preferredcomonomer and one or both of VF and E to form a preferred copolymer.Also preferably, only one of VF and E is used to form a copolymer.

Polymers containing a single CF₂═CF(OR_(f))SO₂F type monomer and asingle cyclic or cyclizable perfluorinated monomer, which are alsopreferred, can be analyzed for mole percent repeat units by doing anelemental analysis of the polymer for C, H and S if the copolymercontains only one of VF and E. This is because the CF₂═CF(OR_(f))SO₂Ftype monomer is the only source of sulfur in the copolymer, and E or VFis the only source of hydrogen in the copolymer when Y is F. If repeatunits derived from both E and VF are present in the copolymer acombination of the elemental analysis plus a H¹ NMR, which can readilydetermine the molar ration of VF and E derived repeat units can be usedto determine the molar ratios of repeat units in the copolymer. All ofthe calculations to determine the ratios of repeat units in thecopolymer can be carried out using standard, well known, chemicalstoichiometric methods.

The polymers can be made by typical liquid (often water) phase freeradical polymerization, see for instance U.S. patent application Ser.No. 14/334,605, U.S. Provisional Applications 62/159,646, 62/159,668,and 62/262,169 (now PCT applications ______, respectively), all of whichare hereby included by reference.

Preferably the various forms of the copolymer described herein(referring to what exactly “Y” is, especially when Y is a Group 11 metalcation) are so-called “glassy” copolymers. By that is meant thecopolymer has no melting point above about 30° C. with a heat of fusionof 3 J/g or more when measured by Differential Scanning calorimetryusing ASTM Test D3418-12e1 using a heating and cooling rate of 10°C./min, and measured on the second heat. Also a glassy copolymer has aGlass Transition Temperature (Tg) above about 40° C., more preferablyabout 40° C. The Tg is measured according to ASTM Test D3418-12e1 at aheating and cooling rate of 10° C./min, and the Tg is taken as themidpoint (inflection point) of the transition on the second heat.Preferably the Tg is less than about 220° C., because for instance ifthe Tg is too high it may be difficult to dissolve the polymer to form acoating or layer.

As noted above, the originally formed sulfonyl fluoride containingpolymer may be modified to form a sulfonic acid containing polymer, or ametal sulfonate salt of the polymer, an ionomer. Group 11 metalionomers, especially silver ionomers, are particularly useful inmembranes for the separation of alkenes from alkanes, see for instanceU.S. patent application Ser. No. 14/334,605, U.S. ProvisionalApplications 62/159,646, 62/159,668, and 62/262,169 (now PCTapplications ______, respectively), A. van Zyl, et al., Journal ofMembrane Science, 133, (1997), pp. 15-26, O. I. Eriksen, et al., Journalof Membrane Science, 85 (1993), pp. 89-97, and A. J. van Zyl, Journal ofMembrane Science, 137 (1997), pp. 175-185, and U.S. Pat. No. 5,191,151,all of which are hereby included by reference. Membranes containingdense layers of one or more Group 11 metal ionomers of the presentcopolymers have been shown to have excellent permeance and/orselectivity in the separation of alkenes from alkenes. Separations ofalkenes from alkene/alkane mixtures can be done with mixtures in eitherthe gas or liquid phase, it is preferred to carry out the membraneseparation of alkene/alkane mixtures in the gas phase and/or usinghumidified gas streams. To carry out such separations, a driving forceis usually applied across the membrane.

In the Examples certain abbreviations are used, and they are:

HFPO—hexafluoropropylene oxide (For preparation of HFPO dimer peroxidesee U.S. Pat. No. 7,112,314, which is hereby included by reference).

PDD—perfluoro(2,2-dimethyl-1,3-dioxole)

SEFVE—CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F

PPSF—CF₂═CFOCF₂CF₂SO₂F

VF—vinyl fluoride (H₂C═CHF)

Determination of Permeance and Selectivity for Alkene/Alkane Separations

For determinations of permeance (GPU, reported in units of sec/cm²·s·cmHg) and selectivity the following procedure was used. A 47 mm flat discmembrane was punched from a larger flat sheet 3 inch composite membrane.The 47 mm disc is then placed in a stainless steel cross flow testingcell comprised of a feed port, retentate port, a sweep inlet port, and apermeate port. Four hex bolts were used to tightly secure the membranein the testing cell with a total active area of 13.85 cm².

The cell was placed in a testing apparatus comprising of a feed line, aretentate line, a sweep line, and a permeate line. The feed consisted ofa mixture of an olefin (alkene) (propylene) gas and a paraffin (alkane)(propane) gas. Each gas was supplied from a separate cylinder. Forolefin, polymer grade propylene (99.5 vol % purity) was used and forparaffin, 99.9 vol % purity propane was used. The two gases were thenfed to their respective mass flow controllers where a mixture of anycomposition can be made. The standard mixing composition was 20 vol %olefin and 80 mol % paraffin at a total gas flow rate of 200 mL/min. Themixed gas was fed through a water bubbler to humidify the gas mixturebringing the relative humidity to greater than 90%. A back pressureregulator is used in the retentate line to control the feed pressure tothe membrane. The feed pressure was normally kept at 60 psig (0.41 MPa)after the back pressure regulator the gas is vented.

The sweep line consisted of a pure humidified nitrogen stream. Nitrogenfrom a cylinder was connected to a mass flow controller. The mass flowcontroller was set to a flow of 300 mL/min. The nitrogen was fed to awater bubbler to bring the relative humidity to greater than 90%. Afterthe bubbler the nitrogen was fed to the sweep port of the membrane tocarry any permeating gas through to the permeate port.

The permeate line consisted of the permeated gas through the membraneand the sweep gas as well as water vapor. The permeate was connected toa three way valve so flow measurements could be taken. A Varian® 450 GCgas chromatograph (GC) with a GS-GasPro capillary column (0.32 mm, 30 m)was used to analyze the ratio of the olefin and paraffin in the permeatestream. The pressure in the permeate side was typically between 1.20 and1.70 psig (8.3 to 11.7 kPa). Experiments were carried out at roomtemperature.

During experiment the following were recorded: feed pressure, permeatepressure, temperature, sweep-in flow rate (nitrogen+water vapor) andtotal permeate flow rate (permeate+nitrogen+water vapor).

From the results recorded the following were determined: all individualfeed partial pressures based on feed flows and feed pressure; allindividual permeate flows based on measured permeate flow, sweep flows,and composition from the GC; all individual permeate partial pressuresbased on permeate flows and permeate pressures. From these thetransmembrane partial pressure difference of individual component werecalculated. From the equation for permeance

Q _(i) =F/(A·Δp _(i))

wherein, Q_(i)=permeance of species ‘i’, F_(i)=Permeate flow rate ofspecies ‘i’ Δp_(i)=transmembrane partial pressure difference of species‘i’, and A is the area of the membrane (13.85 cm²), the permeance(Q_(i)) was calculated.

Example 1 Synthesis of PDD/VF/SEFVE (Feed Ratio 100:100:150) Copolymerand Hydrolysis

Into a 150 mL stainless steel pressure vessel, after argon purging for 5minutes, were added a magnetic stirring bar, 3.66 g PDD, 10.04 g SEFVE,12 mL of Vertrel® XF, 0.6 mL of HFPO dimer peroxide solution (0.12M),and then charged 0.69 g of vinyl fluoride gas at 0° C. The reactionmixture was sealed in the pressure vessel and stirred at roomtemperature in a water bath. After 3 hours of reaction, the reactionvessel was opened to ambient air, 10 mL acetone and 40 mL methanol wasadded to the reaction mixture. The resulting gel like precipitate wastransferred to a glass dish and dried in oven at 100° C. overnight toyield 5.5 g PDD/VF/SEFVE terpolymer as a colorless solid (Tg 37° C.).

Into a 250 mL round bottom flask, were added 3.75 g of the terpolymersynthesized in the previous paragraph, 20 mL deionized water, 60 mL ofmethanol, 1.85 g ammonium carbonate and a magnetic stirring bar. Thereaction mixture was stirred and maintained at 50-60° C. After overnightreaction, a clear solution was obtained. 80 mL 2.0 M hydrochloric acidwas added to the mixture and methanol in the mixture was evaporatedunder heating to form a gel like precipitate. The liquid was decantedand 50 mL of 2.0 M hydrochloric acid was added and stirred for 30minutes. The liquid was decanted and 80 mL of deionized water was addedand then stirred for 30 minutes. After the liquid decanting, the waterwashing was repeated twice and the solid residue was dried in a vacuumoven at 60° C. for 3 hours. A brownish solid (2.7 g) containing freesulfonic acid groups was obtained.

Example 2 Synthesis of PDD/VF/SEFVE (Feed Ratio 100:200:150) Copolymerand Hydrolysis

Into a 150 mL stainless steel pressure vessel, after argon purging for 5minutes, were added a magnetic stirring bar, 3.66 g PDD, 10.04 g SEFVE,15 mL of Vertrel® XF, 0.6 mL of HFPO dimer peroxide solution (0.12M),and then charged 1.38 g of vinyl fluoride gas at 0° C. The reactionmixture was sealed in the pressure vessel and stirred at roomtemperature in a water bath. After 5.5 hours of reaction, the reactionvessel was opened to ambient air, 10 mL acetone and 40 mL methanol wasadded to the reaction mixture. The resulting gel like precipitate wastransferred to a glass dish and dried in oven at 100° C. overnight toyield 9.1 g PDD/VF/SEFVE terpolymer as a colorless solid (Tg 18° C.).Anal: Found: C, 24.92; H, 0.55; S, 5.01. Intrinsic viscosity (in Novec®HFE-7200 at 25° C.): 0.389 dL/g. From the elemental analysis, thepolymer composition was estimated as 21% PDD, 43% VF and 37% SEFVE.

Into a 250 mL round bottom flask, were added 5.8 g of the terpolymersynthesized in the previous paragraph, 20 mL deionized water, 80 mL ofmethanol, 2.0 g ammonium carbonate and a magnetic stirring bar. Thereaction mixture was stirred and maintained at 50-60° C. After overnightreaction, a clear solution was obtained. 80 mL 2.0 M hydrochloric acidwas added to the mixture and methanol in the mixture was evaporatedunder heating to form a gel like precipitate. The liquid was decantedand 50 mL of 2.0 M hydrochloric acid was added and stirred for 30minutes. The liquid was decanted and 80 mL of deionized water was addedand then stirred for 30 minutes. After the liquid decanting, the waterwashing was repeated twice and the solid residue was dried in a vacuumoven at 60° C. for 3 hours. A brownish solid (4.6 g) containing freesulfonic acid groups was obtained.

Example 3 Synthesis of PDD/VF/PPSF (Feed Ratio 100:100:150) Copolymerand Hydrolysis

Into a 150 mL stainless steel pressure vessel, after argon purging for 5minutes, were added a magnetic stirring bar, 3.66 g PDD, 6.3 g PPSF, 12mL of Vertrel® XF, 0.6 mL of HFPO dimer peroxide solution (0.12M), andthen charged 0.96 g of vinylidene fluoride gas at 0° C. The reactionmixture was sealed in the pressure vessel and stirred at roomtemperature in a water bath. After overnight reaction, the reactionvessel was opened to ambient air, 10 mL acetone and 40 mL methanol wasadded to the reaction mixture. The resulting gel like precipitate wastransferred to a glass dish and dried in oven at 100° C. overnight toyield 6.0 g PDD/VF/PPSF terpolymer as a colorless solid (Tg 58° C.).

Into a 250 mL round bottom flask, were added 4.0 g of the terpolymersynthesized in the previous paragraph, 20 mL deionized water, 60 mL ofmethanol, 1.5 g ammonium carbonate and a magnetic stirring bar. Thereaction mixture was stirred and maintained at 50-60° C. After overnightreaction, a clear solution was obtained. 80 mL 2.0 M hydrochloric acidwas added to the mixture and methanol in the mixture was evaporatedunder heating to form a gel like precipitate. The liquid was decantedand 50 mL of 2.0 M hydrochloric acid was added and stirred for 30minutes. The liquid was decanted and 80 mL of deionized water was addedand then stirred for 30 minutes. After the liquid decanting, the waterwashing was repeated twice and the solid residue was dried in a vacuumoven at 60° C. for 3 hours. A slight brownish solid (3.0 g) containingfree sulfonic acid groups was obtained.

Example 4 Membrane Formation and Testing

A solution was prepared using 0.200 g of polymer from example 1 and 20%by weight of silver nitrate in isopropanol to form a 2% polymersolution. A substrate was prepared by coating a 0.3 wright % solution ofTeflon® AF2400 (available from the DuPont Co, Wilmington, Del. 19898,USA) (for further information about Teflon® AF, see P. R. Resnick, etal., Teflon AF Amorphous Fluoropolymers, J. Schiers, Ed., ModernFluoropolymers, John Wiley & Sons, New York, 1997, p. 397-420, which ishereby included by reference) in Fluorinert® 770 (available from 3MCorp., 3M Center, Sty. Paul, Minn., USA) on a PAN350 membrane made byNanostone Water, 10250 Valley View Rd., Eden Prairie, Minn. 53344, USA)(It is believed that the PAN350 membrane is made from polyacrylonitrileand it is believed that this is a microporous membrane). The coating ofthe silver ionomer was done at <30% relative humidity. Similar membraneswere formed from the polymers from examples 2 and 3. Permeability andselectivity results are shown in Table 1

TABLE 1 Permeance (GPU) Polymer from propane propylene SelectivityExample 1 2.70 125.81 46.7 Example 2 4.65 282.44 60.8 Example 3 2.5161.56 75.3

Example 5 Synthesis of PDD/Ethylene/SEFVE Copolymer and Hydrolysis

A pressure reactor that comprised an Ace Glass pressure tube (60-mL) wasassembled in a fume hood. The pressure tube had PTFE #25 and #7Ace-thread top- and side-addition ports, respectively. A hole throughthe top-port plug was threaded and the top-port was connected to a ¼″stainless steel union cross (Parker®). A thermocouple was mountedthrough the cross fitting, which also connected the reactor to a 3-waystainless steel inlet valve and ¼″ stainless steel tubing to a pressuregauge and relief (100-psig). The reactor was magnetically stirred andwas leak tested with 80-psig nitrogen prior to operation. Apolycarbonate safety shield was placed in front of the reactor whenpressurized. Perkadox® 16 (150-mg) and Vertrel® HFE-4310 (18-mL) wereadded through the side port. The reactor was chilled using liquidnitrogen to less than −40° C. SEFVE (10.5-g) and PDD (7.5-g) were addedby syringe through the side port. The stirred reactor was de-gassedwhile cold by briefly evacuating until bubbling indicative of boiling(out gassing) was observed. The reactor was back-filled with argon. Thedegassing was repeated two more times with the reactor remaining undervacuum after the last degassing. Ethylene was added in increments as thereactor warmed with oil bath heating. A constant 50-psig ethylenepressure was maintained as the reactor was stirred at 43 to 45° C. for 5hours. The reactor was depressurized and the contents were purged withnitrogen prior to transferring into a tarred 250-mL wide-mouth jar. Thejar was loosely capped and excess monomers and solvent were carefullyremoved by vacuum oven drying (65° C.) to constant weight (yield=7.8-g).The polymer was colorless and transparent. The intrinsic viscosity wasmeasured by Ubbelohde viscometry in Novec® HFE-7200 at 25° C. and was0.28-dL/g. Reflectance FTIR spectroscopy showed absorbances at 1466-cm¹′and 2850 to 2960-cm¹′ that were indicative of SO₂F and CH groups in thepolymer, respectively. Anal. Found: C, 25.67; H, 0.79; S, 4.47. From theelemental analysis, the polymer composition was estimated as 28% PDD,42% ethylene and 30% SEFVE.

Polymer Hydrolysis. 4.04-g of the polymer was hydrolyzed with 2.5-g ofKOH dissolved in a mixture of 75-mL of methanol and 8-mL of Novec®HFE-7200. The polymer dissolved as it hydrolyzed with heating up to 60°C. for 3 hours. The resulting solution was transparent and very slightlyyellow. The solution was poured into a large dish and the solvents wereslowly evaporated. The polymer was removed from the dish and washed withwater on a filter funnel, acid exchanged with three successive portionsof 1-M nitric acid, and water washed to remove excess acid. The whitepolymer was vacuum oven dried (50° C.) and Reflectance FTIR showed thatthe SO₂F absorbance at 1466-cm⁻¹ had disappeared. 1.5-g of thehydrolyzed and acid exchanged polymer was dissolved to approximately 5%in isopropanol and gently roll milled for 1.5 hours with 1.5-g ofAmberlyst® 15 ion exchange resin, to ensure complete acid exchange. Thesolution was syringe filtered (1-μm glass fiber) and the solids contentof the filtered solution was determined gravimetrically by hot platedrying (110° C.). Solution aliquots were diluted (˜3×) with excessisopropanol and were titrated with 0.0200-M aqueous sodium hydroxide toa phenolphthalein end-point. The equivalent weight was 1157-g/mole forthe polymer free acid.

1. A copolymer, consisting essentially of repeat units derived from amonomer of the formula CF₂═CF(OR_(f))SO₂F, one or more cyclic orcyclizable perfluorinated monomers, and one or both of vinyl fluorideand ethylene, wherein R_(f) is perfluoroalkylene or ether containingperfluoroalkylene having 2 to 20 carbon atoms, and provided that repeatunits derived from CF₂═CF(OR_(f))SO₂F are at least one mole percent oftotal repeat units, units derived from one or more cyclic or cyclizableperfluorinated monomers are at least 1 mole percent of total repeatunits, and repeat units derived from both ethylene and vinyl fluorideare in total at least 1 percent of total repeat units.
 2. The copolymeras recited in claim 1 wherein said repeat unit derived fromCF₂═CF(OR_(f))SO₂F has the formula

wherein Y is fluorine, —OH, or —OM wherein M is a univalent metalcation.
 3. The copolymer as recited in claim 2 wherein Y is —OM, and Mis a silver cation Ag⁺.
 4. The copolymer of claim 1 where said cyclic orcyclizable perfluorinated monomer isperfluoro(2,2-dimethyl-1,3-dioxole).
 5. The copolymer as recited inclaim 4 wherein CF₂═CF(OR_(f))SO₂F is one or more of CF₂═CFOCF₂CF₂SO₂F,CF₂═CFOCH₂CF₂CF₂SO₂F, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F,CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F and CF₂═CFOCF₂CF₂SO₂F.
 6. The copolymer asrecited in claim 5 wherein repeat units from only one type of monomerwith the formula CF₂═CF(OR_(f))SO₂F is present.
 7. The copolymer asrecited in claim 1 wherein repeat units derived from CF₂═CF(OR_(f))SO₂Fare about 10 mole percent to about 40 mole present of total repeat unitsin the polymer, repeat units derived from one or more cyclic orcyclizable perfluorinated monomers are about 5 mole percent to about 30mole present of total repeat units in the polymer, and the total repeatunits derived from ethylene and vinyl fluoride are about 10 mole percentto about 60 mole present of total repeat units in the polymer.
 8. Thecopolymer as recited in claim 7 where said cyclic or cyclizableperfluorinated monomer is perfluoro(2,2-dimethyl-1,3-dioxole), and therepeat units derived from CF₂═CF(OR_(f))SO₂F is one ofCF₂═CFOCF₂CF₂SO₂F, CF₂═CFOCH₂CF₂CF₂SO₂F, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F,CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F and CF₂═CFOCF₂CF₂SO₂F.
 9. The copolymer asrecited in claim 8 wherein said repeat unit derived from CF₂═CF(ORf)SO₂Fhas the formula

wherein Y is fluorine, —OH, or —OM wherein M is a univalent metalcation.
 10. The copolymer as recited in claim 9 wherein Y is —OM, and Mis a silver cation Ag+.
 11. The copolymer as recited in claim 1 whichconsists essentially of repeat units derived from a monomer of theformula CF₂═CF(OR_(f))SO₂F, one or more cyclic or cyclizableperfluorinated monomers, and one or both of vinyl fluoride and ethylene,wherein Rf. is perfluoroalkylene or ether containing perfluoroalkylenehaving 2 to 20 carbon atoms.
 12. A process for the separation of alkenesfrom alkanes in a gaseous stream using a membrane to carry out saidseparation, wherein the improvement comprises, using a membranecomprising a least one dense layer of a Group 10 metal ionomer of acopolymer of any one of claims 2, 3, 9 or
 10. 13. The process as recitedin claim 12 wherein said Group 11 metal is silver.
 14. A membranecomprising at least one dense layer of a Group 11 metal ionomer of acopolymer of any one of claims 2, 3, 9 or
 10. 15. The membrane asrecited in claim 14 wherein said Group 11 metal is silver.
 16. Thecopolymer of claim 2 where said cyclic or cyclizable perfluorinatedmonomer is perfluoro(2,2-dimethyl-1,3-dioxole).
 17. The copolymer asrecited in claim 16 wherein CF₂═CF(OR_(f))SO₂F is one or more ofCF₂═CFOCF₂CF₂SO₂F, CF₂═CFOCH₂CF₂CF₂SO₂F, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F,CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F and CF₂═CFOCF₂CF₂SO₂F.
 18. The copolymer asrecited in claim 17 wherein repeat units from only one type of monomerwith the formula CF₂═CF(OR_(f))SO₂F is present.
 19. The copolymer ofclaim 3 where said cyclic or cyclizable perfluorinated monomer isperfluoro(2,2-dimethyl-1,3-dioxole).
 20. The copolymer as recited inclaim 19 wherein CF₂═CF(OR_(f))SO₂F is one or more of CF₂═CFOCF₂CF₂SO₂F,CF₂═CFOCH₂CF₂CF₂SO₂F, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F,CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F and CF₂═CFOCF₂CF₂SO₂F.
 21. The copolymer asrecited in claim 20 wherein repeat units from only one type of monomerwith the formula CF₂═CF(OR_(f))SO₂F is present.
 22. The copolymer ofclaim 2 wherein repeat units derived from CF₂═CF(OR_(f))SO₂F are about10 mole percent to about 40 mole present of total repeat units in thepolymer, repeat units derived from one or more cyclic or cyclizableperfluorinated monomers are about 5 mole percent to about 30 molepresent of total repeat units in the polymer, and the total repeat unitsderived from ethylene and vinyl fluoride are about 10 mole percent toabout 60 mole present of total repeat units in the polymer.
 23. Thecopolymer as recited in claim 22 where said cyclic or cyclizableperfluorinated monomer is perfluoro(2,2-dimethyl-1,3-dioxole), and therepeat units derived from CF₂═CF(OR_(f))SO₂F is one ofCF₂═CFOCF₂CF₂SO₂F, CF₂═CFOCH₂CF₂CF₂SO₂F, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F,CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F and CF₂═CFOCF₂CF₂SO₂F.
 24. The copolymer asrecited in claim 23 wherein said repeat unit derived fromCF₂═CF(ORf)SO₂F has the formula

wherein Y is fluorine, —OH, or —OM wherein M is a univalent metalcation.
 25. The copolymer as recited in claim 24 wherein Y is —OM, and Mis a silver cation Ag+.
 26. The copolymer of claim 3 wherein repeatunits derived from CF₂═CF(OR_(f))SO₂F are about 10 mole percent to about40 mole present of total repeat units in the polymer, repeat unitsderived from one or more cyclic or cyclizable perfluorinated monomersare about 5 mole percent to about 30 mole present of total repeat unitsin the polymer, and the total repeat units derived from ethylene andvinyl fluoride are about 10 mole percent to about 60 mole present oftotal repeat units in the polymer.
 27. The copolymer as recited in claim26 where said cyclic or cyclizable perfluorinated monomer isperfluoro(2,2-dimethyl-1,3-dioxole), and the repeat units derived fromCF₂═CF(OR_(f))SO₂F is one of CF₂═CFOCF₂CF₂SO₂F, CF₂═CFOCH₂CF₂CF₂SO₂F,CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂SO₂F andCF₂═CFOCF₂CF₂SO₂F.
 28. The copolymer as recited in claim 27 wherein saidrepeat unit derived from CF₂═CF(ORf)SO₂F has the formula

wherein Y is fluorine, —OH, or —OM wherein M is a univalent metalcation.
 29. The copolymer as recited in claim 28 wherein Y is —OM, and Mis a silver cation Ag+.